Mpeg video recording medium and reproduction apparatus

ABSTRACT

The invention relates to an MPEG video recording medium and a reproduction apparatus for the reconstruction of missing data sequences of a video data stream. Scratches and other defects of the recording medium cause interruptions or disturbances in the data stream read from the recording medium, which can be corrected only to a limited extent by conventional error correction methods, such as the Reed-Solomon Code, for example. Therefore, an MPEG video recording medium is provided on which, with respect to an original I frame, at least one copy or a similar I frame is recorded on the recording medium for the reconstruction of missing or erroneous data sequences of a video data stream. The replacement I frames are arranged in the outer area, intermittently or within a predetermined area in the program area on the recording medium and do not influence the reproduction of the recording medium on conventional reproduction apparatuses. In a reproduction apparatus for the reconstruction of missing or erroneous data sequences of a video data stream from an MPEG video recording medium, provision is made of error detection means for determining the sector address of a missing or erroneous I frame, which are used to start a search for a copy or a similar I frame on the recording medium, and provision is made of control means by which a missing or erroneous I frame in the original data stream is replaced by the copy or the similar I frame for the reconstruction of missing or erroneous data sequences of the video data stream and is reproduced by a video decoder.

The invention relates to an MPEG video recording medium and areproduction apparatus for the reconstruction of missing data sequencesof a video data stream.

MPEG video recording media, such as, for example, a video-CD orvideo-DVD, are characterized in that a continuous data stream isrecorded on them in accordance with the MPEG1 video standard or MPEG2video standard. In this case, sequences of pictures are subdivided intogroups designated as GOP, each group of pictures beginning with an Iframe, with is also designated as an intraframe and whose informationforms a prerequisite for the reproduction of the subsequent pictures inthis group. The I frame is followed by B frames and P frames containingdifference information with respect to the I frame, with which thepictures following the I frame are generated. B frames are bidirectionalframes and P frames are also designated as predicted frames. Missing ordisturbed I frames then prevent the representation of the subsequentpictures. Scratches and other defects of the recording medium causeinterruptions or disturbances in the data stream read from the recordingmedium, which can be corrected only to a limited extent by conventionalerror correction methods, such as the Reed-Solomon Code, for example.ECMA standard 267 for DVD specifies, for example, that the diameter ofair bubbles must not be greater than 100 μm and the diameter ofso-called black spots must not be greater than 300 μm. It is demanded,moreover, that the total length of defects greater than 30 μm ought notto exceed a magnitude of 300 μm and that only six such defects arepermitted.

Therefore it is an object of the invention to provide a recording mediumand a reproduction apparatus which enable a reconstruction of themissing data sequences of the video data stream despite disturbed ormissing I frames. Moreover, despite special properties of the recordingmedium, the intention is. also to enable a reproduction of the originaldata stream on conventional reproduction apparatuses.

This object is achieved by features specified in independent claims.Advantageous refinements are specified in dependent claims.

One aspect of the invention provides for additional information itemscomprising additional I frames or replacement I frames to be stored onthe MPEG video recording medium. These I frames may be a copy of Iframes contained in the original data stream or similar I frames with asmaller data volume, which are provided for the reconstruction ofmissing data sequences of the video data stream. This additionalinformation is recorded on the recording medium at one or at a pluralityof distances from the original I frame. What is achieved by the physicaldistance on the recording medium is that, in the case of a disturbed Iframe in the original data stream, the said I frame can be partly orcompletely reconstructed. The physical distance from the original Iframe is achieved by providing a separate data stream for additional Iframes, which data stream is integrated section by section into thecontinuous data stream or is recorded following the original datastream. Information about the location of the additional informationitems is stored either on the recording medium or in a recording orreproduction apparatus provided for recording media of this type. MPEGvideo recording media with additional I frames and information about therecording location of these additional I frames can be used both inconventional reproduction apparatuses and in reproduction apparatusesspecifically provided for these recording media.

In order to reduce the additional data volume, it is provided that, withrespect to the original I frame, similar I frames are used asreplacement I frames. A reduced data volume is achieved by using, asreplacement I frames, by way of example, an image of smaller picturesize, i.e. with a reduced spatial resolution, or a black/white pictureinstead of a colour picture.

The reproduction of recording media which have one or a plurality ofcopies or similar I frames in addition to the original I frame is madepossible in conventional reproduction apparatuses by providing theadditional information items on the recording medium in specificallyprovided MPEG data streams with a dedicated data stream number or asso-called user data, which are ignored by conventional reproductionapparatuses.

In an apparatus for the reproduction of information stored on MPEG videorecording media, for the reconstruction of missing data streamsequences, it is provided that the absence of an I frame is detected andthe missing or erroneous I frame in the data stream is replaced by acopy or a similar I frame. The copy or the similar I frame is providedas additional information on the recording medium. This results in anincreased reliability of the complete reproduction of information storedon optical recording media.

A damaged or missing I frame which is to be replaced is detected byevaluating a discontinuity in the data stream, which is ascertained invarious ways. In accordance with one embodiment, the sector numbering ismonitored, while another embodiment evaluates a scanning device signalwhich signals the non-readability of a sector. Moreover, it is providedthat the decoder uses the transmitted picture size to determine whetheran I frame is incomplete or damaged. In these cases, the start sectornumber of the damaged I frame is already known and can be used forfinding an I frame that is additionally provided on the recordingmedium. In accordance with this embodiment, a table is provided whichspecifies the location at which the I frame which can be used asreplacement for this start sector number is stored. In the case of MPEG2video data streams, it is possible, by way of example, to use the userdata area into which a sector number for an additional I frame isentered for each group of pictures. Such a table is also advantageouslyused to detect missing I frames. This is made possible by comparing thesequence of the start sector numbers of the I frames with the entries inthe table. In this case, the number of I frames to be replaced can beascertained at the same time.

Furthermore, the absence of an I frame can be ascertained from the factthat a predetermined number of pictures in a group is exceeded, or inthat the distance between time stamps provided in the data stream isevaluated.

After the identification of the damaged or missing I frame, the I frameprovided as replacement on the recording medium is requested andinserted into the data stream in accordance with the requirements. Thedecoded replacement I frame is then used for the reconstruction of themissing data sequence.

The MPEG video recording medium may be a read-only, a write-once or awrite-many optical recording medium. In the case of read-only recordingmedia, the replacement I frames can be provided in the outer area,intermittently or within a predetermined area in the program area on therecording medium. In other words, on account of the addressing that canbe used, the replacement I frames can be arranged both after and beforethe original I frame. Therefore, in the case of read-only recordingmedia, replacement I frames can be arranged on the recording medium insuch a way that the reproduction of the original data stream onconventional reproduction apparatuses is not influenced.

A predetermined writing strategy is to be complied with in the case ofwrite-once and write-many recording media. A data stream to be recordedis generally buffered, however, so that it can be analysed with regardto I frames contained therein. After a predetermined number of groups ofpictures, copies of I frames contained in the original data stream orsimilar I frames with respect to the original I frames are then recordedin sectors which follow the group of pictures. Moreover, during therecording of the replacement I frames, a table is formed which containsthe start sector number of the original I frames and the sector numberof the copy or similar I frames. This table is then recorded after thereplacement I frames or at a distance therefrom on the recording medium.This results in an intermittent recording of replacement I frames which,on account of the concordance formed with the table, are used asrequired for reconstruction of missing or erroneous data sequences. Inprinciple, it is also possible to record all the replacement I framesand the abovementioned table at the end of the data stream or at the endof the recording on the recording medium.

The fact that one or a plurality of copies of different or identicalquality level to the original I frames are provided on the recordingmedium advantageously enables the reconstruction of missing or damageddata sequences during the reproduction of MPEG video information.

Scratches or other disturbances of optical recording media which, due tothe fact that I frames cannot be read, usually lead to interruptions inthe picture reproduction do not adversely affect the picturereproduction as a result of the use of the replacement I frames. As aresult, a complete reproduction of recorded video information is madepossible despite damaged recording media. The physical distance at whichthe replacement I frames are provided with respect to the original Iframes is larger by a multiple than what is allowed by the customarymeasures for error correction, such as, for example, Reed-Solomon andchannel bundling. Consequently, it is possible to eliminate evenrelatively large and multiply occurring errors which can no longer becorrected by the customary error correction.

In principle, there are various possibilities for advantageouslyrefining and developing the present invention. In this respect,reference is made on the one hand to the claims and on the other hand tothe following explanation of exemplary embodiments of the invention withreference to drawings.

The invention is explained in more detail below with reference toexemplary embodiments in drawings.

In the figures:

FIG. 1 shows imperfections on optical recording media,

FIG. 2 shows frames of a video data stream,

FIG. 3 shows an arrangement of replacement information items on anoptical recording medium,

FIG. 4 shows a schematic sketch of a first reproduction apparatus forMPEG video recording media,

FIG. 5 shows a block diagram of a second reproduction apparatus for MPEGvideo recording media,

FIG. 6 shows an arrangement of additional or replacement informationitems in the original data stream.

FIG. 7 shows the content of tables which are used to produce aconcordance with respect to copies or similar I frames, and

FIG. 8 shows a schematic sketch relating to the structure of a videodata stream.

In FIG. 1, four different types of imperfections, as often occur afterrelatively long use or on careless handling of optical recording mediaOD, are illustrated on two optical recording media OD. Examples of suchimperfections are fingerprints E1, dust E2 or scratches which have alinear E3 or radial E4 profile. During the reproduction of informationrecorded on the optical recording medium OD, such imperfections lead toread errors or to interruptions in the scanned data stream. If the datastream is an MPEG data stream containing an MPEG video data stream, thesectors of the data stream typically form a group of pictures, as isillustrated in FIG. 2.

The individual picture of a video sequence is also designated as a frameand, as standard, the picture data rate of the digital video standard is167 megabits per second. Without compression, video information couldthen be recorded only for approximately four minutes on a video-DVDhaving a storage capacity of 4.7 GB. However, video contains amultiplicity of redundant information since each individual pixel of apicture is assigned digital information items relating to the brightnessand colour. Since unmoving picture components do not change over arelatively long period of time, it is entirely sufficient to code thechanges in a picture or frame. Accordingly, an MPEG data stream containsso-called I frames I, which, independently of other frames, containinformation about an entire individual picture, and also B frames B andP frames P. A B frame B utilizes preceding frames in order to calculatethe compressed data content of the frames, and P frames P represent thedifference in the I frames. A P frame analyses the preceding frames andthereby estimates where objects should be situated in the next frame. Asillustrated in FIG. 2, an I frame I is followed by a respective numberof difference pictures which necessarily require the start frame I1 inorder to form the individual pictures. If an I frame I1 fails to appear,for example because it cannot be read from the recording medium OD andcannot be recovered by a conventional error correction, the subsequentpictures B, B, P, B, B, P, B, B of the group of pictures cannot beformed either. The reproduction of an entire data sequence would therebybe disturbed Therefore, an MPEG video recording medium is provided onwhich, for the reconstruction of a group of pictures, a replacementinformation item or a replacement I frame I1* for a disturbed I frame I1is recorded in order to prevent or at least reduce interruptions in thepicture progression. As illustrated in a schematic sketch in FIG. 3,this replacement information can be kept within the recording area A ofthe original data stream or else separately in a recording area Boutside the recording area A of the original data stream on the opticalrecording medium OD. The replacement information items are provided onthe recording medium OD in such a way that a reproduction by means ofconventional reproduction apparatuses is not impeded or influenced. Forthis purpose, for the replacement information items, provision is madeof a separate data stream with a dedicated data stream number which isformed for example with a StreamID, not part of the DVD standard, or theadditional or replacement items are recorded in a so-called user dataarea which is situated before a group of individual pictures, alsodesignated as GOP, and is not reproduced as video information. As aresult, in conventional apparatuses, replacement information items areignored, or skipped as errors, even when nested in the original datastream. Preferably, as illustrated in FIG. 6, additional or replacementinformation items are inserted in the original data stream at a distanceof a plurality of groups of pictures GOP. It is appropriate to store aplurality of replacement I frames I* in groups GOP*, so that, by way ofexample, twenty replacement I frames I1* . . . I20* form a group ofpictures GOP*a. For write-once and write-many recording media, thedistance between these replacement I frames I* groups GOP* results fromthe minimum distance from the original picture information, which inturn results from the maximum error correction length of the errorcorrection method chosen for the recording on the optical recordingmedium OD, and the size of the write memory which, during the recordingoperation, keeps the replacement I frames I* group GOP* until it can bestored on the optical recording medium OD.

FIG. 7 shows, by way of example, the content of tables TB1, TB2 whichare used to produce a concordance with respect to the copies or similarI frames I* In this case, it is assumed that these tables TB1, TB2, astable TB, are recorded after the conclusion of a recording operation asa data stream which is provided with a private data stream identifierTableID. This private data stream identifier TableID, which isprivate_stream_id, for example, is likewise ignored and skipped byconventional reproduction apparatuses.

In this structure, the first table TB1, which contains the data streamidentifier TableID and also the number of entries EntryTag[MAXENTRIES]and a pointer to a previous table PreviousTable, is provided inparticular for the recording and the reproduction of a plurality ofmutually independent video data streams.

However, the pointer to a previous table PreviousTable also makes itpossible to find replacement I frames I* in other groups GOP* ofreplacement I frames I* within a video data stream without the need tokeep a whole table at the end of the recording medium for this purposeor for a plurality of video data streams. The conclusion of a recordingis formed by a second table TB2 of the table TB directly after the lastgroup GOP* of replacement I frames In* that are kept.

As illustrated in FIG. 8, the pointer to the presence of a table TB canbe kept in a file system FS provided for conventional reproductionapparatuses or in a separate directory.

The concordance table in accordance with the second table TB2 in FIG. 7contains the positions for original I frames I as ReferenceFrameSectorIDand for replacement I frames I* as RedundantFrameSectorID and also anidentifier FrameInfoFlags which reveals how these replacement I framesI* are to be conditioned in order that they can be used for thereconstruction of the original data stream.

A video data stream with additional information items then has astructure illustrated in a schematic sketch in FIG. 8. The file systemFS is followed by a video data stream sequence SMVS which contains, asvideo MV, the original data stream and replacement I frames I* and alsoa table TB. An area EONS following the video data stream sequence SMVSmay then either be empty or a following video data stream sequence SMVSmay be provided.

The construction of a reproduction apparatus for the reconstruction ofmissing data sequences of an original video data stream from an MPEGvideo recording medium with replacement information is illustrated as aschematic sketch in FIG. 4. The MPEG data stream scanned from an opticalrecording medium OD by an optical scanning device PU is firstly fed to amemory, a so-called track buffer TB, connected to the scanning devicePU. Connected to the track buffer TB is a sector analysis device SA-U,which separates the data stream into individual streams for video andaudio, which are then fed to the corresponding MPEG decoders for videoVD-U and audio AD-U for reproduction.

If there are disturbances on the recording medium which cannot beeliminated by conventional error correction methods, gaps occur in theMPEG data stream and lead to disturbances in individual pictures orentire groups of pictures. These gaps are detected either by analysis ofthe sectors in the sector analysis device SA-U or during the decoding ofthe pictures in the video decoder VD-U and an item of information aboutthe sector address of the missing or erroneous I frame I is communicatedto an error processing unit EH-U. The error processing unit EH-U theninitiates a check to determine whether additional or replacementinformation items which can eliminate or reduce the disturbance in thepicture progression are available on the optical recording medium OD.The replacement information items are then requested from the scanningdevice PU by the error processing unit EH-U with a sector request SR andare inserted or entered into the picture progression in the videodecoder VD-U.

In accordance with a second embodiment illustrated as a block diagram inFIG. 5, a navigation manager NM is provided which comprises functionsfor the supervision of a user interface of the reproduction device. Thenavigation manager NM starts an access to the optical recording mediumOD by the start positions of MPEG data streams on the optical recordingmedium OD being requested by means of a file system manager FM whichcommunicates bidirectionally with the navigation manager NM. For thispurpose, the file system manager FM transfers this request to a pick-upmanager PU-M, which thereupon initiates a transmission of a data streamwith the scanning device PU. The requested data are communicated to thepick-up manager PU-M by the scanning device PU and entered into a trackbuffer TB. The file system manager FM reads these sectors in the trackbuffer TB and from them determines the start positions of the MPEG datastreams which it transfers to the navigation manager NM. The startpositions of the MPEG data streams are also used to carry out atransmission of an MPEG data stream from the optical recording medium ODto the corresponding MPEG decoders for video VD-U and audio AD-U for thepurpose of reproduction. In this case, the navigation manager NMtransfers the start position of the MPEG data stream to a requestcontrol unit RC, which causes the pick-up manager PU-M to read acontinuous MPEG data stream from the recording medium OD by means of theoptical scanning device PU.

The MPEG data stream thus passes from the optical recording medium ODvia the scanning device PU into the pick-up manager PU-M, which entersthe data under supervision into the track buffer TB and already executesfirst measures for monitoring the continuity of the data stream. In thiscase, in a targeted manner, returns are executed for repeated read-in inorder to close or reduce gaps in the data stream, and messages arecommunicated to the downstream sector analysis device SA-U in order toindicate a gap in the data stream. The sector analysis device SA-Uadditionally receives a list with start addresses in the track buffer TBwhich show the location at which the sectors of the MPEG data streamentered by the pick-up manager PU-M were stored. The sector analysisdevice SA-U distributes the individual partial data streams of the MPEGdata stream with the aid of this list and the contents of the sectors.Partial lists are produced which are forwarded to the downstream MPEGdecoders for video VD-U and audio AD-U.

In addition, the sector analysis device SA-U extends the data streamchecking already performed by the pick-up manager PU-M by using existinginformation in the data stream, such as the sector number or the startidentifiers of the MPEG data sections, to find out whether an MPEG videodata stream has a gap in which there were I frames 1. If this is thecase, an error notification is communicated to the error processing unitEH-U. Furthermore, instances where a range is exceeded, e.g. at the endof an MPEG data stream, can be captured and communicated to thenavigation manager NM via the request control unit RC.

The video decoder VD-U receives the partial list of sector positions ofthe MPEG data stream in the track buffer TB which contain video sectors.If a missing or damaged I frame I is detected by this stage, for exampleby evaluation of the time stamps or comparisons of the number ofmacroblocks present with the picture size transferred in the video datastream, an error notification is likewise communicated to the errorprocessing unit EH-U. The error processing unit EH-U initiates an accessby the request control unit RC to the table with the additionalinformation items, which is then communicated via the pick-up managerPU-M and the sector analysis device SA-U from the scanning device PU tothe error processing unit EH-U. The error processing unit EH-Udetermines from the table a possible replacement representation of themissing or damaged I frame I and starts a renewed enquiry for a sectorstream via the request control unit RC and the pick-up manager PU-M withthe scanning device PU from the optical recording medium OD.

The data stream which then follows is communicated from the scanningdevice PU and the pick-up manager PU-M to the sector analysis deviceSA-U. If the error in the data stream has already been detected in thisstage, the replacement I frame I1* can be entered into the original datastream. If a larger gap with a plurality of missing I frames I1, I2, . .. was involved, each replaced I frame I is signed off in the errorprocessing unit EH-U, which thereupon checks whether further replacementI frames I2* must still be requested. If this is not the case, the errorprocessing unit EH-U can request a new data stream which starts with thesector number at which the gap was detected. Normal processing of theoriginal MPEG data stream is resumed at this point.

If the error in the data stream was detected in the video decoder VD-U,the error processing unit EB-U likewise requests a table. The startaddress for a replacement I frame I* which emerges from this table issubsequently determined and this replacement I frame I* is requested.The decoded replacement I frame I* can then replace a missing or damagedI frame I in the event of a renewed request of the data stream of thegroup of pictures. If a plurality of I frames I are affected in thiscase, too, it may be necessary for the error processing unit EH-U torequest replacement I frames I*, which are decoded and reproduced, untila valid or original MPEG video data stream again passes into the videodecoder VD-U.

As a result, a complete reproduction of recorded video informationwithout interruption is made possible despite damaged recording mediahaving imperfections which cannot be corrected by conventional errorcorrection methods.

The embodiments described here are specified only as examples and aperson skilled in the art can realize other embodiments of the inventionwhich remain within the scope of the invention.

1. MPEG video recording medium for the reconstruction of missing orerroneous data sequences of a video data stream, wherein, on the MPEGvideo recording medium, with respect to an original I frame, provisionis made of at least one copy or a similar I frame on the recordingmedium for the reconstruction of missing or erroneous data sequences ofa video data stream in a reproduction apparatus.
 2. MPEG video recordingmedium according to claim 1, wherein the copy or a similar I frame withrespect to the original I frame is arranged both at a logical and at aphysical distance on the recording medium.
 3. MPEG video recordingmedium according to claim 1, wherein copies or similar I frames withrespect to the I frames of an original data stream are arranged in amanner combined in groups, inserted into the original data stream, onthe recording medium.
 4. MPEG video recording medium according to claim1, wherein a concordance information item is stored on the recordingmedium and specifies the location on the recording medium at which acopy or a similar I frame with respect to the original I frame isarranged.
 5. MPEG video recording medium according to claim 4, whereinthe concordance information item is arranged in a user data area orafter a group of copies or similar I frames on the recording medium. 6.Reproduction apparatus for the reconstruction of missing or erroneousdata sequences of a video data stream from an MPEG video recordingmedium, wherein in the reproduction apparatus, provision is made oferror detection means for determining the sector address of a missing orerroneous I frame in the original data stream, which are used to start asearch for a copy or a similar I frame on the recording medium, andprovision is made of control means by which a missing or erroneous Iframe in the original data stream is replaced by the copy or the similarI frame for the reconstruction of missing or erroneous data sequences ofthe video data stream and is reproduced by a video decoder. 7.Reproduction apparatus according to claim 6, wherein the error detectionmeans is a sector analysis device connected to a track buffer or is thevideo decoder, which are connected to an error processing unit providedas control means.
 8. Reproduction apparatus according to claim 6,wherein the error detection means is a pick-up manager, which enters thedata stream from the recording medium into a track buffer, a sectoranalysis device or the video decoder, in which time stamps or the numberof macroblocks contained in the data stream are evaluated. 9.Reproduction apparatus according to claim 6, wherein the control meansis an error processing unit which is connected to error detection meansand, with a sector request, requests the copy or the similar I framefrom the recording medium and inserts it in the video decoder byreplacement of the missing or erroneous I frame in the original datastream for the reconstruction of missing or erroneous data sequences ofthe video data stream.
 10. Reproduction apparatus according to claim 6,wherein the control means is a navigation manager to which a file systemmanager and a request control unit are connected bidirectionally, whichare driven by error detection means and, with a pick-up manager, requestthe copy or the similar I frame from the recording medium and missing orerroneous I frames in the original data stream are replaced in a trackbuffer connected to the pick-up manager or in the video decoder by thecopy or the similar I frame by means of the file system manager or bymeans of a sector analysis device for the reconstruction of missing orerroneous data sequences of the video data stream.